A digital audio tape recorder (hereinafter referred to as DAT) for recording, for example, sound in PCM (Pulse Code Modulation) system, is adapted to record PCM data having error-correcting codes added thereto in order to correct or interpolate errors in the PCM data caused by scratches or adhesion of dust on the magnetic tape. Moreover, since a correction capability for one data sequence is restricted, the PCM data is interleaved, and recorded in a dispersed manner so that errors are not concentrated on one specific data sequence. Therefore, in reproduction, after correcting the data for errors, the dispersed data is returned to its original sequence. The process for returning the dispersed data to its original sequence is referred to as "deinterleaving".
On the other hand, some DATs, such as those for professional use, have an editing function for replacing a part of recorded sound with another sound. The above editing function is referred to as "punch in/out". In order to execute the editing function, as illustrated in FIG. 5(a), there are installed a advanced reproduction head 15, recording head 16 and a signal processing circuit including a memory 17. The advanced reproduction head 15 is disposed at the upstream side of a magnetic tape 18 so as to read out PCM data from the magnetic tape 18. The recording head 16 is disposed at the downstream of the advanced reproduction head 15, with a predetermined distance therefrom. The memory 17 stores the PCM data read out by the advanced reproduction head 15. In the above arrangement, punch-in/out operations are performed as follows.
First, a normal reproducing operation will be described hereinbelow. PCM data on the magnetic tape 18 is read out by the advanced reproduction head 15 (additionally, in FIG. 5(a) and FIG. 6(a), rectangular areas arrayed on the memory 17, magnetic tape 18 and punch-in data 19 which will be described later, as well as numerals attached to the areas represent data blocks and block numbers respectively.) The PCM data having been read out is successively stored in the memory 17. The PCM data stored in the memory 17 is on the one hand reproduced to be released as sound after having been applied thereto predetermined signal processing operations such as error correcting, and is on the other hand successively read out from the memory 17 and re-recorded on the magnetic tape 18 through the recording head 16. In this case, the arrangement is made such that signal processing time required for the PCM data to be read out from the magnetic tape 18 and re-recorded on the magnetic tape 18 is equal to inter-head travelling time required for the magnetic tape 18 to travel a distance from the advanced reproduction head 15 to the recording head 16. With the arrangement, since the PCM data read out from the magnetic tape 18 is re-recorded on the same position of the magnetic tape 18 where the reading-out operation was performed, the position of the PCM data on the magnetic tape 18 is not changed before and after the re-recording.
Next, in editing operation for rewriting a part of PCM data into another PCM data, an input to the recording head 16 is switched from a reproduced audio signal to an audio signal to replace with (punch-in). Upon finishing the rewriting, the input to the recording head 16 is switched again to the reproduced audio signal from the advanced reproduction head 15 (punch-out), thereby permitting the part of recorded sound to be replaced with another sound. For example, as shown in FIG. 5(a), punch-in data 19 consisting of blocks 0 to 2 are those edited and overwritten on the position corresponding to the blocks 0 to 2 on the magnetic tape 18.
For ideal punch-in/out operations as described above, the interleaving sequence of the data would possess an accurate continuity as is shown in FIG. 5(b), and error correction and interpolation would be performed precisely. Further, by adopting the cross-fade method or the like, a smooth switchover between the reproduced audio signal and the audio signal to replace with may be achieved. Therefore, no noise would be generated at the punch-in point and punch-out point.
However, in actual operations, the inter-head travelling time is not necessarily equal to the signal processing time due to variation of the inter-head distance, deviation of the tape speed, or stretch or shrinkage of the tape after recording. For this reason, as shown in FIG. 6(a), the recording position of the punch-in data 19 is sometimes dislocated from a desired position on the magnetic tape 18 for rewriting. When this happens, as shown in FIG. 6(b), the interleaving sequence of the data shows discontinuity before and after the punch-in/out point. When returned to the original sequence, a discontinuous portion of the data is directly deinterleaved, and therefore it makes unusual data retaining no correlation to the original PCM data existing before and after it. Further, since errors on the discontinuous portion of the data are beyond its error-correction capability, noise is generated during reproduction.
As described above, in order to perform deinterleaving, the following methods (1) and (2) are adopted: (1) data is divided into blocks with respective block numbers attached; (2) when reproducing the data recorded on the tape in a dispersed manner, they are rearranged based on the block numbers. However, lost data due to the dislocation of the recording position (such as that shown in FIG. 6(a) as a block number 3) are all recognized as errors in the interleaving sequence as is shown in FIG. 6(c), and therefore the number of lost data tends to exceed the limitations of the correction and interpolation capabilities. The inclusion of noise into the reproduced sound is due to a number of data which are thus released with errors remaining therein. Moreover, the interleaving sequence of edited data on the tape remains discontinuous such that the error-correcting operation during reproduction must be performed based on the discontinuous interleaving sequence. This results in a lowering of the correction capability even on errors normally produced due to drop-out of data, scratches or dust on the tape, noise, etc.
In the conventional devices, in order to eliminate the above problems, high accuracy and strict performances are required in dimensions of inter-head distance, speed control for the tape, stretch or shrinkage properties of the tape, etc. For this reason, there are presented such problems as follows: work efficiency in assembling the recording-reproduction apparatus is lowered; interchangeability of the magnetic tapes is not fully achieved; it is difficult to maintain enough performances required for the magnetic tapes for a long period.